<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            position: absolute;
            width: 200px;
            height: 200px;
        }
        .xiongda {
            background-color: yellow;
            /* 通过 z-index； 提升叠放级别，默认为0 */
            /* z-index 后不能加单位 */
            /* 只有加定位的盒子才有 z-index 属性 */
            z-index: 1;
        }
        .xionger {
            background-color: tomato;
            /* 数值越大越靠上 */
            z-index: 2;
        }
        .qiangge {
            background-color: saddlebrown;
        }
    </style>
</head>
<body>
    <div class="xiongda">熊大</div>
    <div class="xionger">熊二</div>
    <div class="qiangge">光头强</div>
</body>
</html>